The long-term objective of this research is to identify, isolate and purify the proteins and glycoproteins which mediate the interaction of sperm and egg during sea urchin fertilization. Using antibodies against purified proteins we have shown that a specific 84 Kd glycoprotein of the sperm membrane is involved in induction of the sperm acrosome reaction. We are currently purifying this important protein by preparative methods. We have also found two glycoproteins of 115 and 119 Kd which compose about 50% of the protein of isolated sperm plasma membranes. We propose to purify these sperm membrane components and to determine their function. We are continuing work on sequencing the sperm protein, bindin, which binds the sperm to the egg surface. We have worked out a new method for the isolation of very pure bindin in large quantity. We will continue to study the interaction of bindin with eggs and to isolate the intact bindin receptor. We propose to construct lipid vesicles containing bindin and to study their interaction with the egg (one successful experiment already). The antibody to bindin that we possess will be of great help in these studies. We will examine the presence of adenyl cyclase, phosphodiesterase and calmodulin in the same egg cortex using the new cortex isolation procedure we have developed. We will continue our characterization of the egg surface and the isolation of the bindin receptor from the vitelline layer. The knowledge we will gain by these studies of the gamete surface components involved in fertilization will someday be useful in the development of new strategies of nonhormonal contraception.